Blue Ox Posted March 23, 2019 Share Posted March 23, 2019 I am thinking of putting an exhaust brake on my 2000 e7 460. I have been trying to find out what the maximum allowable exhaust back pressure is for my engine. I run 107000# and could use extra braking on hills. My other option I am considering is a telma retarder. I can find one from a mr688 and am wondering if anyone has installed one? Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/ Share on other sites More sharing options...
david wild Posted March 23, 2019 Share Posted March 23, 2019 Telmas work great, they are used in the coal feilds, lot of braking power. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418838 Share on other sites More sharing options...
Macktech689 Posted March 23, 2019 Share Posted March 23, 2019 I have installed a couple dozen Telma systems and they are pretty straight forward. Is the Telma retarder you are looking at frame or carrier mounted? Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418840 Share on other sites More sharing options...
Blue Ox Posted March 23, 2019 Author Share Posted March 23, 2019 I am looking at a frame mounted one. I have a pacbrake off a c9 that is rated at 40# pressure. I found one place that said no more than 25# on an etech so I don't think I will use it. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418848 Share on other sites More sharing options...
Macktech689 Posted March 24, 2019 Share Posted March 24, 2019 The frame mounted retarder is the best way to go, carrier mounted units caused a lot of problems. Visit telmausa.com and look under the technical support tab, lots of good information, that will give you a idea of what you are getting into. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418892 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 Thanks for the reply. I have been studying their site. I really like the idea of the telma, wish I could see one in operation. I am just weighing the cost of each. I think in the end I would be happier with the telma. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418946 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 Looks like it weighs a decent amount, not sure what maintenance is involved. A traditional engine brake or a butterfly style seems simpler and less maintenance. And weigh less. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418955 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 The telma will add about 700#. The maintenance is not bad, really just the bearings as far as I have found so far. The exhaust brake is simple enough, my concern is the back pressure. I have found one place that says the etech is limited to 25# back pressure. I don't want to have the valves float and hit the piston. I am going to try pacbrake today and see what they say. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418965 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 (edited) I think the butterfly brakes are operated by an air cylinder. I assume you can put an air regulator on it to control the amount of back pressure the brake generates. Find out what # springs the exhaust valves are, and what diameter they are. Run a little math, you'd have to generate enough force to counteract the valve springs to cause valves to float. You'll need to leave a safety factor to ensure the springs can still hold the valves with some force. Your other choice is a traditional Jake brake that opens the exhaust valves at TDC of compression stroke to dump off the combustion energy. Doesn't generate any back pressure, and certainly doesn't take 700# off your payload. Edited March 25, 2019 by JoeH Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418966 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 Pacbrake has a spring on it that controls the back pressure. I just found their application chart that lists the etech being limited to 20#. Don't think that will give much braking . Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418967 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 What back pressure do they list for other brands like Cummins? You might be surprised. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418969 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 Others are 45 to 80#. The pre etech e7 is 45#. I can't figure out why the etech would be so low. I have a jake on the truck and is working as good as expected, just looking to help it. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418971 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 the service manual I have says valve springs are 190 to 210#. That is what is confusing. Why would pacbrake say 20#? Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418975 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 You have to take the 190# and convert it to psi on the surface area of the valve head. If it's a 2 inch diameter, πr^2 is 3.14159. Now take your 20 psi back pressure and you have 60+ pounds of pressure trying to open your valves, which leaves 130 pounds of spring pressure holding them shut. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418976 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 I got the 60 pounds of pressure because it's 20 pounds per square inch and a 2 inch valve has 3.14159 square inches of surface area. If it's a 3 inch valve the surface area jumps to 7 inches, which jumps to 140 pounds of back pressure acting on your valves, leaving only 50 pounds of spring pressure shutting the valves. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418977 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 From what I can find they are 1.573. I should have plenty of spring. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418978 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 My son in law works for ny state dot and says they run exhaust brakes on their macks. Going to try to find more info from them Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418979 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 That's exhaust valve diameter? That has about 1.8-1.9 square inches of surface area, so that's about 40 pounds of pressure. At higher RPMs you need more pounds of spring tension because the valves have less time to close between cycles. 40 # of pressure on the valve leaves you 150# of spring pressure. Of course the back pressure doesn't push on the valve with that 40# until the valve is shut. At fully opened the valve spring might not have much resistance, as the pressure is vented into the cylinder. But, you also have vacuum created on the intake stroke which is acting to pull the exhaust valve open, which is takes from your remaining 150# spring pressure. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418983 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 If the piston generates 20psi vacuum then that's another 40# off your valve spring, leaving you with 110# spring pressure. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418984 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 Would there be another reason for them saying 20#? Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418985 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 Only other thing I could think of is pushing exhaust past turbo seals? Exhaust manifold should have no problem holding that pressure. I would call pacbrake and ask. Get on the phone with a tech or engineer there and ask questions. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418986 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 Just called pacbrake. They said they don't do anything with macks???? I am thinking the chart I found on they're site isn't much value. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418987 Share on other sites More sharing options...
Blue Ox Posted March 25, 2019 Author Share Posted March 25, 2019 Thanks for all the help. I can't find a reason not to use the brake. I'm down for mud season so I have time to look around some more before I install it. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418988 Share on other sites More sharing options...
fjh Posted March 25, 2019 Share Posted March 25, 2019 (edited) 1 hour ago, Blue Ox said: Just called pacbrake. They said they don't do anything with macks???? I am thinking the chart I found on they're site isn't much value. I have been studying their site. I really like the idea of the telma, wish I could see one in operation. I am just weighing the cost of each. I think in the end I would be happier with the telma. I will bring some experience to the table here! Take it for what it is worth! Pre and real early eteck there was An exhast brake Option called Stealth brake!!!! To install this unit we were required to remove valve covers and replace or add valve seals and replace valve springs to install these! Having said that the unit helped on engine braking a fair bit ! We however started having issues with turbos on these the exhaust gasses started over coming the shaft seals on the turbo on long downhill grades pushing the gasses into the base causing horrible blowby issues ! the fix was a special turbo with extra sealing rings on the shaft seal! if you plan on going this route. Don't say you weren't warned!!! Just saying! Telma I have nothing bad to say about this unit , other than the extra weight added they function great! Edited March 25, 2019 by fjh 1 Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-418995 Share on other sites More sharing options...
JoeH Posted March 25, 2019 Share Posted March 25, 2019 A traditional Jake brake is my preference. Simple, tried and true. Doesn't give the most braking, but it's adequate. If it doesn't hold you around 1800 RPMs on the downgrade then you're in too high of a gear for the hill anyways. Quote Link to comment https://www.bigmacktrucks.com/topic/56330-exhaust-back-pressure/#findComment-419000 Share on other sites More sharing options...
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